How about some pointer on using LspCAD?

Discussion in 'Archived Threads 2001-2004' started by Ryan Schnacke, Oct 30, 2001.

  1. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Alright, I've finally downloaded this beauty from Adire's website. And I know that some of you have become very adept at using it. So I thought I'd ask about a few things I'm having trouble with, mostly stuff thats just not explained very well.
    "Watts into 8 ohms" (Measurement Setup) - What about a plate amp that's rated at 4 ohms. Should I divide this rated power by 2 and use that for my 8 ohm number? What if I'm using a seperate amplified channel for each voice coil (100Wx2 @ 8 ohms)? I should list the total power (200W) and select "separate sources" in the driver configuration window, right?
    "Qa" and "Fill %" (Box window) - The manual seems to indicate that Qa is determined exclusively by Fill %, yet you can specify them independantly. And they each have an effect on the curves. What gives?
    "Optimization" (Box window) - I thought I'd start by trying to emulate the Rava design and verify that my results matched the Adire numbers. I put a Shiva in a sealed box and used the "Optimize by table look-up" to get a Q=0.707 box of 64L. Now Adire says the Rava is Q=0.67 in 60L. How'd they manage that? I tried cranking up my fill % but that didn't seem to affect the optimization routine. Have I missed something?
    "Q" - Speaking of alignments, is there a window that or menu option that will calculate the total Q for a design once I'm done tweaking and adjusting?
    "Port air speed" - My second experiment was to try to emulate the Dharman. I put a Shiva in a bass reflex box with 2 ports - minimum diameter 3" and maximum diameter 4.5" to 5". I was guessing on the max diameter number. 109L and tuned to 22Hz. I don't remember the precise port length I was getting but it was around 30 - 35cm (darn those metric units). With 140 watts @ 8 ohms (????) and voice coils in parallel I was getting port speeds over the 15m/s maximum that they recommend. Is that right?
    Sorry so long. But this is interesting stuff and I'd like to learn more about it.
    [Edited last by Ryan Schnacke on October 30, 2001 at 02:14 PM]
     
  2. Isaac C

    Isaac C Stunt Coordinator

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    Hi Ryan,
    quote: What about a plate amp that's rated at 4 ohms. Should I divide this rated power by 2 and use that for my 8 ohm number?[/quote]
    Yes
    quote: What if I'm using a seperate amplified channel for each voice coil (100Wx2 @ 8 ohms)? I should list the total power (200W) and select "separate sources" in the driver configuration window, right?[/quote]
    No -- it is my understanding that you list the applied power for each voice-coil... then yes -- select "Separate Sources."
    quote: "Qa" and "Fill %" (Box window) - The manual seems to indicate that Qa is determined exclusively by Fill %, yet you can specify them independantly. And they each have an effect on the curves. What gives?[/quote]
    Qa is defined to be the absorption losses due to filling material, so yes -- Qa is defined by the amount of fill. As for the reason behind both value's independence in the program, I can only guess that even without any fill, something in the box could still contribute to absorption losses. This possibility, I believe, is allowed for by the program. Now, existing absorption losses without any fill... then adding fill should decrease Qa (if memory serves me well), but lspCAD limits Qa between 3.0 and 100. From my own simulations, there's little difference with values over 100.
    quote: "Optimization" (Box window) - I thought I'd start by trying to emulate the Rava design and verify that my results matched the Adire numbers. I put a Shiva in a sealed box and used the "Optimize by table look-up" to get a Q=0.707 box of 64L. Now Adire says the Rava is Q=0.67 in 60L. How'd they manage that? I tried cranking up my fill % but that didn't seem to affect the optimization routine. Have I missed something?[/quote]
    I'm not familiar with the Rava, so I can't comment on this.
    quote: "Q" - Speaking of alignments, is there a window that or menu option that will calculate the total Q for a design once I'm done tweaking and adjusting?[/quote]
    If there is such a feature, I can't see it as well. But for Vented-Boxes, the book, "Loudspeaker Design Cookbook" by Vance Dickason has the equations to calculate the system Q. The same equations can also be found in the following page (under the Impedance Curve section).
    http://www.geocities.com/f4ier/sbb4.htm Corrections anyone?
    HTH
    Isaac
    ------------------
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    [Edited last by Isaac C on November 01, 2001 at 06:28 AM]
     
  3. Ryan Schnacke

    Ryan Schnacke Supporting Actor

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    Isaac,
    Thanks very much. I'll check out the equations you referenced and try your sub simulator when I get a chance.
     

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